Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$78.92	13.393%	$89.4898	$89.49	$89.50	$89.50
Purchase #2	$44.90	10.853%	$49.773	$49.77	$49.75	$49.80
Purchase #3	$156.48	13.837%	$178.1321	$178.13	$178.15	$178.10
Purchase #4	$135.80	12.304%	$152.5088	$152.51	$152.50	$152.50
Purchase #5	$224.39	6.409%	$238.7712	$238.77	$238.75	$238.80
Purchase #6	$71.49	8.700%	$77.7096	$77.71	$77.70	$77.70
Purchase #7	$41.49	7.258%	$44.5013	$44.50	$44.50	$44.50
7 purchase totals =	$753.47		$830.8858	$830.88	$830.85	$830.90